The present invention relates to an oscillating or swinging device for a dredger of the kind comprising a dredging boom having two relatively movable arms.
A dredger of this kind is known from U.S. Pat. No. 4,242,816. The first arm is generally provided with a platform at one end which it moves over the water bottom in successive steps of approximately one meter. Between steps, this platform remains fixed on the water bottom. The second arm, which possesses a working tool at its end, is articulated to this platform about a substantially vertical axis. This arm is oscillated by a swinging device to execute a sweeping movement with an amplitude of approximately 140.degree. (.+-.70.degree. relative to a middle position).
The swinging device is one of the elements of this type of dredger which is difficult to produce in a simple, robust and economical way.
Disadvantages of the known swinging devices which may be mentioned are those of:
(i) a lack of torque in the extreme position of the second dredging arm when the latter is 70.degree. to port or 70.degree. to starboard; PA1 (ii) a considerable bulk and a complex structure; and PA1 (iii) a cost price which is consequently high.
In one embodiment of the prior art, swinging is effected by means of one or more jacks, each having a body which is fixed to the platform by means of a swivel pin. The piston rod of the jack is articulated to the pivoting part of the swinging device, this part being fixed to the second arm.
In the extreme positions, that is to say in the position wherein the angle between the jack and the swinging dredging arm approaches 180.degree., there is a deficiency of torque. Since the body of the jack is fixed to the platform, the size of the platform is governed by this factor. The overall structure of the dredger is consequently made heavier, and the cost price is increased.